Background Arteriovenous fistulas (AVFs) often fail to mature, but the mechanism of AVF nonmaturation is poorly understood. Arterial microcalcification is common in patients with chronic kidney disease (CKD) and may limit vascular dilatation, thereby contributing to early postoperative juxta-anastomotic AVF stenosis and impaired AVF maturation. This study evaluated whether preexisting arterial microcalcification adversely affects AVF outcomes. Study Design Prospective study. Setting & Participants 127 patients with CKD undergoing AVF surgery at a large academic medical center. Predictors Preexisting arterial microcalcification (â‰¥ 1% of media area) assessed independently by von Kossa stains of arterial specimens obtained during AVF surgery and by preoperative ultrasound. Outcomes Juxta-anastomotic AVF stenosis (ascertained by ultrasound obtained 4-6 weeks postoperatively), AVF nonmaturation (inability to cannulate with 2 needles with dialysis blood flow 300 mL/min for 6 sessions in 1 month within 6 months of AVF creation), and duration of primary unassisted AVF survival after successful use (time to first intervention). Results Arterial microcalcification was present by histologic evaluation in 40% of patients undergoing AVF surgery. The frequency of a postoperative juxta-anastomotic AVF stenosis was similar in patients with or without preexisting arterial microcalcification (32% vs 42%; OR, 0.65; 95% CI, 0.28-1.52; P = 0.3). AVF nonmaturation was observed in 29%, 33%, 33%, and 33% of patients with <1%, 1% to 4.9%, 5% to 9.9%, and 10% arterial microcalcification, respectively (P = 0.9). Sonographic arterial microcalcification was found in 39% of patients and was associated with histologic calcification (P = 0.001), but did not predict AVF nonmaturation. Finally, among AVFs that matured, unassisted AVF maturation (time to first intervention) was similar for patients with and without preexisting arterial microcalcification (HR, 0.64; 95% CI, 0.35-1.21; P = 0.2). Limitations Single-center study. Conclusions Arterial microcalcification is common in patients with advanced CKD, but does not explain postoperative AVF stenosis, AVF nonmaturation, or AVF failure after successful cannulation.